2013 American Geophysical Union  San Francisco, USA  H24E-02

1. The GEWEX LandFlux Initiative: development and analysis of a global land surface heat flux product Matthew McCabe1, Eric Wood2, Carlos Jimenez3, Diego Miralles4, Ali Ershadi5, Miaoling Liang2, Brigitte Mueller6, Sonia Seneviratne6and Chris Kummerow7 + MANY OTHER CONTRIBUTORS & DATA PROVIDERS 1 King Abdullah University of Science and Technology, Saudi Arabia 2Princeton University, United States of America 3 Observatoirede Paris, France 4University of Bristol, United Kingdom 5 University of New South Wales, Australia 6 ETH Zurich, Switzerland 7 Colorado State University, United States of America 2013 American Geophysical Union San Francisco, USA H24E-02 Presented to WDAC by J. Schulz, EUMETSAT

2. GEWEX Reference Products Validation BSRN Validation Ships and Buoys Validation Towers

3. Value added by GDAP: GEWEX Integrated Products Validation BSRN Validation Ships and Buoys Common Output with uncertainty Common Ancillary Data Validation Towers +

4. LandFLUX Introduction • GEWEX Data and Assessments Panel (GDAP): • Goal: Develop global observationally based products to allow independent water and energy cycle assessment (1984-2007). • : • Challenge(s): Heat fluxes cannot be remotely detected – need an interpretive model to infer them: • What model to use? • What forcing to choose? • What scale and resolution is appropriate? • How to evaluate and assess model (and forcing) data?

5. Background 4 • Challenge: heat fluxes do not have a unique signature that can be remotely detected, so satellite observations need to be combined by a model (process-based, empirical,….) to infer them. Sink for vapour ATMOS. DEMAND ATMOSPHERE Source of energy SATELLITE OBSERVATIONS MODEL ET Short/Long-wave radiation Source of water WATER SUPPLY SOIL VEGETATION

6. Identifying an Interpretive Model • Range of potential model types available: • Many options with different data/parameter needs • Is one model able to reproduce all biome/land types? • Opportunity to undertake model inter-comparison PT-JPL SEBS GLEAM PM-Mu Fisher et al. 2008 Su, 2002 Miralles et al. 2010 Mu et al. 2007; 2011

7. Tower and Model Forcing Data Forcing and common parameters - led by Princeton Grid based data derived from a combination of reanalysis, satellite products and VIC model data • Tower Data • Flux tower and site information from http://www.fluxdata.org/DataInfo/ • Meteorology • Vegetation height • Radiation components • LST from LWU • Satellite based NDVI • INTERCEPTION!!!???

8. Progress in Product Assessment • Developing a long-term record of global heat fluxes • Examine global scale response • Assess region-to-catchment scales • Evaluate model grid-to-tower based observations

9. Progress in Global Assessment Global scale evaluation and inter-comparison:

10. Progress in Global Assessment • Findings from global scale inter-comparisons: • Large number of existing ET datasets (GCM, LSM, reanalysis) • Observation based products largely consistent with others • Globally consistent but regionally variable • Product synthesis provides a benchmark dataset • See http://www.iac.ethz.ch/url/research/LandFlux-EVAL

11. Progress in Global Assessment Findings from global scale inter-comparisons: SEBS PM-Mu GLEAM PT-JPL [mm day-1] 1984-2007 mean annual ET (soil+transpiration) 0 1 2 3 4 5 6

12. Progress in Global Assessment Findings from global scale inter-comparisons: SEBS PM-Mu GLEAM PT-JPL [mm day-1] Differences of annual mean ET with 4-model annual average -2 -1 0 1 2

13. Progress in Regional Assessment • Basin scale inter-comparison and latitudinal change • Generally good agreement at basin scales (P-Q vs ET) • Considerable variation in tropics (interception issue)

14. Progress in Regional Assessment • Findings from regional scale inter-comparisons: • Comparisons stratified by water or energy limited regions Dry-Wet Index (P/PET) Categories: Extreme dry: <0.05 Dry : 0.05～0.2 Semi-dry: 0.2～0.5 Semi-wet: 0.5～1.0 Wet: 1.0～1.5 Moist: 1.5～2.0 Extreme wet: >2.0

15. Progress in Grid-Tower Assessment • Intercomparison of the GEWEX LandFLUX models: • Common forcing: LandFLUX V0 and 116 (45) FLUXNET sites • Models assessed at 3 hourly, daily and monthly scales • 7 land cover types and 7 climate types PT-JPL SEBS GLEAM PM-Mu Fisher et al. 2008 Su, 2002 Miralles et al. 2010 Mu et al. 2007; 2011

16. Model Inter-comparison Results • Statistical analysis based on Taylor diagrams • Scatter plots are largely useless: need better metrics • All models improve when run with tower data • Need to examine within biome/climate variation Model clustering/convergence with increasing temporal resolution 45 Common Towers Monthly 3 hourly Daily

17. Single Model Response to Forcing What is the impact of different forcing data? |R| .77 .78 .80 .74 .51 .80 GLEAM: AIRS + SRB daily + CMORPH GLEAM with ERA-Interim inputs GLEAM with Princeton + SRB (3h) ERA-Interim NCEP-NCAR GLEAM with Princeton + SRB (daily) Reference data based on 200 Fluxnetsites from Diego Miralles

18. Summary and Conclusion Some take home messages: A difficult product to derive, as it merges products with their own uncertainties and models with their own assumptions. Global products require multiple metric and multiple evaluation scales (incl. spatial and temporal). Ground data have their own issues. Model performance linked to metric, scale and zone/type- model sensitivity to forcing v’s forcing uncertainty. Issue of forcing quality constrains achievable accuracy. Influence of seasonality on model response (not shown)- better performance spring/autumn v’ssummer/winter. No model works everywhere, every time!- an ensemble product/model weighting/new models? Data being pre-released for ongoing assessment

19. Future Work and Opportunities Still some outstanding challenges: Production of sensible heat and ground heat fluxes Frozen/snow-covered areas are still missing Ongoing algorithm development (soil moisture stress term, better surface resistance/vegetation params) … need to keep in mind: Satellite products respond to different needs, e.g., LandFLUX is targeting climatological applications and consistency with other GDAP products opening opportunities: Water and energy budget studies with GDAP products Needed community involvement and product development (Version 2+…) LandFLUX Version 0 to be released in July, 2014